17. PHYSICS OF THE CIRCULATION SYSTEM (PART 2) Flashcards
- What is Aortic Narrowing and Arterial Stenosis
(Narrowing)?
- they are the localised narrowing in the arterial lumen
- they are a result of atherosclerosis
ATHEROSCLEROSIS = a condition that develops when a
sticky substance (plaque) builds up
inside your arteries
- What is Arterial Stenosis often related to?
- it can be genetic
- blood related
- lifestyle related
- With early Atherosclerosis, what are the features that are specific to Aortic Stenosis?
- mechanical injury
- With intermediate Atherosclerosis, what are the features that are specific to Aortic Stenosis?
- prominent early mineralisation
- nodule formation
- With Late Atherosclerosis, what are the features that are specific to Aortic Stenosis?
- heavy calcification
- leaflet stiffening
- With early Atherosclerosis, what are the features that are specific to both Aortic Stenosis and Athero-Sclerosis?
- endothelial injury
- low shear stress
- inflammation
- With intermediate Atherosclerosis, what are the features that are specific to both Aortic Stenosis and Athero-Sclerosis?
- degradation of the extracellular matrix
- lipid deposition
- inflammation
- With late Atherosclerosis, what are the features that are specific to both Aortic Stenosis and Athero-Sclerosis?
- calcification
- fibrosis
- inflammation
- With early Atherosclerosis, what are the features that are specific to Athero-Sclerosis?
- fatty streak
- With intermediate Atherosclerosis, what are the features that are specific to Athero-Sclerosis?
- foam cells
- smooth muscle cells
- proliferation
- With late Atherosclerosis, what are the features that are specific to Athero-Sclerosis?
- plaque raptures
- thrombus
- FATAL
- Which ratio is Stenosis quantified by?
- As / Ao
- this is called the Area Ratio
- it is expressed as a % of area occlusion
- How is the relation between the pressure drop across the stenosis (▵P) and the flow of blood (Q) mathematically expressed?
STENOTIC RESISTANCE INCREASES WITH FLOW
STENOSIS:
- caused additional quadratic pressure loses
THIS IS ON TOP OF THE ALREADY EXISTING:
- linear and proportional pressure loses
BOTH THE FLOW AND THE AREA APPEAR AS:
- quadratic terms
- this is an important aspect of the
hemodynamics of a narrowing
- What does the highlighted term represent?
- this represents the viscous losses
- these happen during Stenosis
- What does the highlighted term represent?
- this represents the losses due to Turbulence
NB: Kt is an empirical coefficient
: it is equal to 1.5
- What happens with Severe Stenosis?
- the area occlusion % is higher than 85%
- the turbulent loses dominate
- it results in significant resistance to blood flow
- this is potentially harmful
- it prevents adequate blood supply to distal beds
- When the stenosis length (l) is assumed to be extremely small, what can be said about the pressure drop?
- the pressure drop is proportional to the flow rate squared
- the pressure drop is inversely related to the square of the cross-sectional area
- What can be said about the pressure drop in laminar flow?
- the pressure drop is proportional to the flow rate
- What is a 90% stenosis 5 times more severe than?
- an 80% stenosis
- this is in terms of the pressure drop for a similar flow
- What causes the complaints from Ischemia to arise suddenly?
ISCHEMIA = a condition in which blood flow and oxygen
are restricted/reduced in a part of the body
- the non linear effect that occurs when the narrowing
becomes more severe - this is typically found in a stenosis of 60% to 70%
- According to Bernoulli’s Equation, what can be said about pressure at high velocities?
- the pressure is low
- the pressure in the narrow section may decrease to lower values
- What is the result of stenosis occurring in vessels with Compliant walls?
- there is a decrease in transmural pressure
- this leads to extra narrowing
- this worsens the situation
TRANSMURAL = existing or occurring across the entire
wall of an organ or blood vessel
- Read through Summary 1.
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- yes
- Read through Summary 2.
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- Read through Summary 3.
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- Read through Summary 6.
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- Read through Summary 7.
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- Read through Summary 8.
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